1. Field of the Invention
The present invention relates to the field of a disk drive, and more particularly, to a servowriting method for writing a servo pattern to a disk medium.
2. Description of the Related Art
In general, a disk drive represented by a hard disk drive is configured to write or read data to/from a disk medium by means of a magnetic head (hereinafter, referred to merely as a “head”).
The disk drive incorporates a servo system that moves the head for writing or reading data to a target position (target track) on the disk medium for positioning.
The servo system, in which a microprocessor (CPU) of the disk drive serves as a main component thereof, uses servo information (servo pattern data) that has previously been written to the disk medium to perform head positioning control (servo operation).
In the disk drive, the servo pattern data is written, as a magnetic signal, to servo areas (servo sectors) arranged on the disk medium at regular intervals.
The manufacturing process of the disk drive includes a servowrite process in which the servo pattern data is written to the disk medium. As a servowriting method, a self-servowriting method is available in addition to a method of using a dedicated servowriter (or servo track writer: also referred to as an “STW”).
The self-servowriting method, in which the disk drive writes the servo pattern data to the disk medium in a self-reliant manner without using an external positioning mechanism such as a positioner, is advantageous in terms of manufacturing cost. In general, the self-servowriting process is carried out in a state where a top cover is attached to the main body of the disk drive.
Of the self-servowriting methods, in particular, prior art called the additive servowriting method has been disclosed (refer to, for example, Jpn. Pat. Appln. KOKAI Publication No. 8-212733).
The additive servowriting method is a method of using a head incorporated in the disk drive to determine the timing of the disk in the disk rotation direction and the head position in the radial direction of the disk medium, thereby writing servo pattern data to the disk medium in a self-reliant manner.
The method described above is advantageous in terms of manufacturing cost. In addition, the method can write servo pattern data while constantly observing relative positions between the disk medium and head in the radial direction of the disk medium, performing the writing operation with high accuracy.
The additive servowriting method positions (performs tracking of) a read head element to the servo pattern data that has been written by a write head element included in the head, then moves the head to the writing position of next servo pattern data, and writes the next servo pattern data by means of the write head element.
In this manner, the servo pattern data are sequentially written from, for example, the innermost to outermost part of the disk medium. The servo pattern data obtained by the additive servowriting operation is referred to as an “additive servo pattern” for convenience in some cases.
In the method described above, the additive servo pattern needs to have signal quality good enough to position the read head element correctly in order to determine the next writing position. However, in a servowriting process, influence of disturbance or the like makes it difficult to write all the additive servo patterns in a good condition.
If an additive servo pattern having quality so bad as to exceed an allowable range has been written, writing accuracy in the additive servo pattern may be adversely affected, which may prevent the subsequent writing operation in practice. If the following additive servowriting operation is started again from the beginning, efficiency in the servowrite process may be decreased.